A conventional in-wheel motor drive device has been disclosed in Japanese Unexamined Patent Publication No. 2006-258289 (patent document 1). According to the in-wheel motor drive device disclosed in the patent document 1, a drive motor, a speed reducer to receive driving force from the drive motor and reduce rotation speed thereof and output it to the wheel side, and a wheel hub member coupled to an output shaft of the speed reducer are coaxially arranged. This speed reducer has a cycloidal speed reducing mechanism, so that a high speed reduction ratio is obtained as compared with a planetary gear type of speed reducing mechanism which is common as a conventional speed reducer. Therefore, this is considerably advantageous in that torque required for the drive motor can be small, and the in-wheel motor drive device can be reduced in size and weight. In addition, according to this cycloidal speed reducing mechanism, an outer pin is rotatably supported by a needle roller bearing with respect to a casing. Therefore, this is considerably advantageous in that contact resistance between a curve plate and the outer pin can be greatly reduced, and a torque loss of the speed reducer can be cut.
According to the cycloidal speed reducing mechanism in the patent document 1, as shown in FIG. 3, a disk-shaped eccentric part 25a is mounted on an input shaft of the speed reducer which is coupled to a rotation shaft of the drive motor so as to be eccentric with respect to an axis O of the input shaft. More specifically, an axial center O2 of the eccentric part 25a is eccentric with respect to the axis O of the input shaft by an eccentric amount of “e”. A curve plate 26a is mounted on an outer circumference of the eccentric part 25a with a rolling bearing 41 therebetween, and the eccentric part 25a rotatably supports the curve plate 26a. The axial center O2 serves also as an axial center of the curve plate 26a. An outer circumference of the curve plate 26a is composed of a waveform curve and has radially recessed waveform parts 33 provided at circumferentially regular intervals. The curve plate 26a is surrounded by a plurality of outer pins 27 which engage with the recessed parts 33 and are circumferentially arranged around the axis O.
In FIG. 3, as the eccentric part 25a rotates anticlockwise on the sheet surface together with the input shaft, the eccentric part 25a make a revolution motion around the axis O, so that the recessed parts 33 of the curve plate sequentially abut on the outer pins 27 in a circumferential direction. As a result, as shown by arrows, the curve plate 26a receives a load Fi from the plurality of outer pins 27 and rotates clockwise.
In addition, a plurality of through holes 30a are circumferentially arranged around the axial center O2 in the curve plate 26a. An inner pin 31 coupled to the output shaft of the speed reducer arranged coaxially with the axis O passes through each through hole 30a. Since an inner diameter of the through hole 30a is sufficiently larger than an outer diameter of the inner pin 31, the inner pin 31 does not disturb the revolution motion of the curve plate 26a. Thus, the inner pin 31 extracts the revolution motion of the curve plate 26a and rotates the output shaft. At this time, the output shaft has higher torque and lower rotation speed than the input shaft, so that the curve plate 26a receives a load Fj from the plurality of inner pins 31 as shown by arrows in FIG. 3. The loads Fi and Fj are combined and a bearing load Fs is provided.
According to the cycloidal speed reducing mechanism, since a rotation difference is large between the input shaft and the output shaft, and driving force of the vehicle is transmitted, the bearing load Fs is high, so that it is necessary to appropriately lubricate the rolling bearing 41 in order to implement a stable operation without causing a burn. More specifically, a lubricant oil hole to supply a lubricant oil is provided in the rolling bearing 41 which includes a rolling body, an outer ring member provided on the outer diameter side with respect to the rolling body, and an inner ring member provided on the inner diameter side with respect to the rolling body. It is conceivable that the lubricant oil hole is arranged in an outer circumference track surface of the inner ring member 42 or an inner circumference track surface of the outer ring member with which the rolling body is in rolling contact.
In the case where the lubricant oil is supplied from the radial outer side to the inner circumference track surface of the rolling bearing 41, the lubricant oil could be splashed due to high rotation speed, or outflow toward the radial outer side due to centrifugal force, so that it is difficult to distribute the lubricant oil in the whole rolling bearing. Thus, the lubricant oil is preferably supplied from the radial inner side to the outer circumference track surface of the rolling bearing 41. More specifically, the radially extending lubricant oil hole is arranged in the eccentric part 25a, and a radial outer side end of the lubricant oil hole is arranged in the outer circumference track surface of the inner ring member 42. Thus, the lubricant oil is supplied from the inside of the input shaft to the rolling bearing 41 through the lubricant oil hole of the eccentric part 25a. 